| OCR Text |
Show 1884.] MR. J. B. SUTTON ON THE CRANIAL ARCADE. 569 examined some cases of cleft-palate and can support Albrecht's statements, but in the normal condition there is only one centre for each premaxillary bone. The discrepancy may be thus explained :- the premaxilla is originally developed in membrane, and at some little distance from the median line, which, in the foetus, is occupied by the thick cartilage known as the ethmo-vomerine plate. After a time the premaxillary ossifications involve the anterior extremity of this cartilage, so that the inner portions of these bones are really of cartilage origin. If anything interfere to prevent the premaxillary bone or bones meeting the ethmo-vomerine plate, the tip of this cartilage ossifies on its own account, and gives rise to the false notion of two independent centres occurring normally. This fact may be verified easily in the majority of mammals. In other parts of the Three views of the human superior maxilla, to visually express tbe disposition of its four ossific centres. M . Malar centre, Max. Maxillary centre, Pre-M. Pre-maxillary, and Pre.P. Pre-palatine centres. skull instances of a bone arising in membrane and invading cartilage might be quoted in support of m y opinion. The next centre to be considered forms the palate process of the maxilla and a considerable portion of the inner wall. Fig. 1 represents it as an L-shaped piece of bone, forming by means of its horizontal plate the roof of the mouth, whilst its vertical plate extends upwards as far as the orbital surface of the bone. This centre will be referred to throughout this paper as the " pre-palatine " centre. |
